Fluid operated downhole pumps for deep oil wells are known to those skilled in the art as evidenced by the Roeder U.S. Pat. No. 3,453,963, Roeder U.S. Pat. No. 3,703,926, and McArthur U.S. Pat. No. 3,849,030. In the recited Roeder U.S. Pat. No. 3,453,963, there is set forth a double acting pump having an engine spaced from the production pump. Roeder also mentions a valve assembly operating between pistons which are connected together by a control connecting rod having undercut areas formed thereon for supplying fluid to shift the main valve. Accordingly, the up and down sliding movement by the connecting rod occurs inside a control sleeve, such as discussed in Roeder and later on exemplified by the McArthur patent. In both the prior art Roeder and McArthur patents, the connecting rod is provided with an undercut area which functions to operate a main valve located between the opposed engine pistons. The undercut area reduces the tensile strength of the connecting rod and introduces a weakened area which is prone to fracture and break.
Roeder U.S. Pat. No. 3,703,926 illustrates a production piston or plunger which sucks in formation fluid under the production piston on the upstroke and forces the fluid out on the downstroke.
It is often desirable to fabricate the engine and pump pistons as large as possible while making the connecting rod as small as possible so as to achieve a maximum effective piston area. The connecting rod which rigidly connects together the two engine pistons is drastically weakened when provided with an undercut area for engine valve operation. In order to eliminate undercutting the piston connecting rod, the present invention provides a valve assembly unique in design because the main control valve is actuated by fluid flow directed by a pilot control valve rod, and the rod is mechanically actuated by contact made by each end by the engine pistons and more particularly by the exhausting chamber side of the pistons. The main control valve allows power fluid to pass into the high pressure chamber while exhausting spent power fluid out through the center portion of the main control valve. High pressure power fluid never enters the inside portion of the main control valve. This unique pump assembly includes means by which high pressure fluid alternately contacts alternate areas of the main control valve, while the small end is constantly subjected to low pressure fluid on each stroke of the rod system. The main control valve moves in phase with the connecting rod movement. Accordingly, after the main control valve moves to the up position, the rod system is forced up, and after the main control valve moves to the down position, the rod system is forced down. The exhausting side of the engine piston contacts the pilot rod, pushing it into position to either release high pressure fluid above the main control valve or to provide a passage for high pressure to enter above the large area of the main control valve.
The provision of the above improved hydraulically actuated pump assembly enables the incorporation of a new intake and exhaust valve system into the apparatus. Accordingly, the present improvement in downhole pumps provides an engine which can transmit greater forces towards the pumping action each reciprocation of the engine thereof, and furthermore provides improved flow passageways through which the production fluid can flow.